内部类之一

 内部类
在一个类中定义另外一个类，这个类就叫做内部类或内置类 (inner class) 。
内部类可以让我们将逻辑上相关的一组类组织起来，并由外部类(outer class)来控制内部类的可见性。
当我们建立一个inner class时，其对象就拥有了与外部类对象之间的一种关系，这是通过一个特殊的this reference形成的，使得内部类对象可以随意的访问外部类中所有的成员。

class Out
...{
            private int index=100;
            class Inner
            ...{
                    private int index=50;
                        public void print()
                        ...{
                                int index=30;
                                    System.out.println(index);
                                    System.out.println(this.index);
                                    System.out.println(Out.this.index);
                  }
            }
            public void print()
            ...{
                        Inner inn=new Inner();
                        inn.print();
            }
}
class OutTest
...{
            public static void main(String[] args)
            ...{
                 Out out=new Out();
                 out.print();
                 
            }
}

 内部类INNER可以看成是OUT类的一个成员变量，MAIN是一个静态的方法，静态方法内部不可以实例化成员变量

class Out
...{
            private int index=100;
            class Inner
            ...{
                    private int index=50;
                        public void print()
                        ...{
                                int index=30;
                                    System.out.println(index);
                                    System.out.println(this.index);
                                    System.out.println(Out.this.index);
                  }
            }
            public void print()
            ...{
                        Inner inn=new Inner();
                        inn.print();
            }
            Inner getInner()
            ...{
                    return new Inner();
            }
            /** *//**public static void main(String[] args)
            {
                 Out out=new Out();
                 Inner inn=out.getInner();//因为Inner是在Out内部的，是可见的
                 //Inner inn=new Inner();内部类INNER可以看成是OUT类的一个成员变量，
                 //MAIN是一个静态的方法，静态方法内部不可以实例化成员变量
                 inn.print();                 
            }*/
}
class OutTest1
...{
            public static void main(String[] args)
            ...{
                 Out out=new Out();
                 //out.print();
                 Out.Inner inn=out.getInner();//因为Inner是在Out内部的，是不可见的
                 inn.print();
                 
            }
}

在方法中定义的内部类，如果要访问方法中定义的本地变量或方法的参数，则变量必须被声明final。
内部类可以声明为private或protected；还可以声明为abstract或final。
内部类可以声明为static的，但此时就不能再使用外部类的非static的成员变量和非static的成员方法；
非static的内部类中的成员不能声明为static的，只有在顶层类或static的内部类中才可声明static成员。

 

class Out
...{
            private int index=100;
            void fn(final int a)//方法内部的内部类无法供该方法外的函数访问
            ...{
                   final int b=0; 局部变量a,b需要被内部类访问的话，必须声明为final
                        /** *//**class Inner//方法内部的内部类
                        {
                                private int index=50;
                                    public void print()
                                    {
                                            int index=30;
                                                System.out.println(index);
                                                System.out.println(this.index);
                                                System.out.println(Out.this.index);
                              }
                        }*/
                        /** *//**if()//条件语句中的内部类
                        {
                                    class Inner
                                    {
                                            private int index=50;
                                                public void print()
                                                {
                                                        int index=30;
                                                            System.out.println(index);
                                                            System.out.println(this.index);
                                                            System.out.println(Out.this.index);
                                          }
                                    }
                      }    */
                      if(true)//条件语句中的内部类
                        ...{
                                ...{//语句快当中的内部类 
                                            class Inner
                                            ...{
                                                    private int index=50;
                                                        public void print()
                                                        ...{
                                                                int index=30;
                                                                    System.out.println(index);
                                                                    System.out.println(this.index);
                                                                    System.out.println(Out.this.index);
                                                                    System.out.println(a);
                                                                    System.out.println(b);
                                                  }
                                            }
                                  }            
                      }        
                      if(true)//条件语句中的内部类
                        ...{
                                class Middle
                                ...{//语句快当中的内部类 
                                      private int index=60;
                                            class Inner
                                            ...{
                                                    private int index=50;
                                                        public void print()
                                                        ...{
                                                                int index=30;
                                                                    System.out.println(index);
                                                                    System.out.println(this.index);
                                                                    System.out.println(Middle.this.index);
                                                                    System.out.println(Out.this.index);
                                                  }
                                            }
                                  }            
                      }                                        
            }            
            public void print()
            ...{
            }
}
class OutTest3
...{
            public static void main(String[] args)
            ...{
                 Out out=new Out();
                /** *//** Out.Inner inn=out.new Inner();
                 inn.print();*/                 
            }
}

 

 

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